This invention relates to halophosphate phosphors activated by divalent europium, said phosphors emitting light normally in the blue region of the emission spectrum when excited by radiations, and a process for producing the same.
Conventional halophosphate phosphors activated by divalent europium have a host crystal structure of the mineral apatite as disclosed in Japanese Patent Appln Kokoku (Post-Exam Publn) Nos. 40604/71 and 33159/73 and can be represented by the formula: EQU 3Sr.sub.3 (PO.sub.4).sub.2.MbCl.sub.2
wherein Mb is at least one member selected from the group consisting of Sr, Ca and Ba; or by the formula: EQU 3Ma.sub.3 (PO.sub.4).sub.2.MbX.sub.2
wherein Ma is an elementary substance of Ca or Ba or a mixture of two or more of Ca, Ba and Sr; X is a halogen; and Mb is as defined above.
But these conventional phosphors are not sufficiently satisfiable in emission efficiency, color tone, and the like in some fields of applications. Further, there is a tendency to lower the brightness due to oxidation of divalent europium during the baking in the air when the phosphors are coated inside of fluorescent lamps, and the like.